In order to use the structures safely for a long time which are difficult to be moved such as a bridge, an express way, an elevated track for a railway, a building, a tank, a machine facility and the like, a coating of painting applied on a surface of a base material (steel material) needs to be periodically peeled off, removed, and re-painted in order to prevent corrosion. As a prior-art method for removing a coating, there were a method by blast treatment such as sandblast for removing a coating by blowing sand, a method of using a coating remover, and a method of using a mechanical tool. In the method by blast treatment, a large quantity of secondary waste is generated. This secondary waste is a mixture of a powder dust of a coating containing harmful matters such as lead, chromium hexavalent, PCB and the like and an abrasive material such as silica sand, garnet and the like, which gives a large load to the environment and requires a large treatment cost. Moreover, since the abrasive material is blown by compressed air, there is a concern that even the base material under a coating layer is damaged. Moreover, there is also a problem of a large noise caused at collision of the abrasive material. The methods of using a coating remover and the mechanical tool, they both have a problem that a treatment area per time is small, which is not efficient, and each has problems that a waste of the agents is generated and the noise is large.
Patent Literature 1 discloses a method of removing a coating by a laser treatment apparatus in order to improve working efficiency and to avoid a risk against the prior coating removal of an outer plate of such as an aircraft fuselage by blowing a highly toxic drug to the coating surface and scraping off the coating film by a manual work. The laser treatment apparatus described in Patent Literature 1 includes a lens for irradiating a laser beam to a surface of a treatment target, a lens supporting mechanism which supports the lens and can adjust a height from the treatment target surface to the lens, and a gas injecting means for blowing gas to a laser irradiation portion. Moreover, it is described that a gas inlet arranged in a box-shaped vessel exhausts the gas in the box-shaped vessel and exhausts the removed matter scattered from the laser irradiation portion. It is also described that a sweeping process for sweeping an irradiation position of the laser beam to a first direction by using a first deflector arranged in an optical path of the laser beam incident to the lens and moving the irradiation position of the laser beam in the first direction within the surface of the treatment target by changing a traveling direction of the laser beam and a second deflector arranged in the optical path of the laser beam incident to the lens and moving the irradiation position of the laser beam in a second direction crossing the first direction within the surface of the treatment target by changing the traveling direction of the laser beam is performed a plurality of times while shifting in the second direction crossing the first direction. It is described that, in such a laser treatment apparatus, a laser irradiation head is mounted on a tip-end of a manipulator arm, and the manipulator arm is controlled by a manipulator body and moves and supports the laser irradiation head to a desired position on the surface of the treatment target.